part of the catchment and is leading to severe ecological
problems and socio-economic upstream–downstream water
user conflicts.
Figure
9
shows the change of several hydrological and
meteorological parameters from the glaciated headwaters
to the official end of the river near Bukhara. As the ele-
vation of the riverbed is steadily decreasing from the Za-
rafshan glacier in the east (2,810 m a.s.l) to the Bukhara
oasis in the west (220 m a.s.l.) the average annual air
temperature is increasing from 4.2 to 15.6
C. The pre-
cipitation shows a different pattern as it is rather deter-
mined by the orography in the catchment. The highest
annual average precipitation rates occur with up to 341 mm
at the foothills of the Turkestan and Zarafshan mountain
ranges near the Uzbek–Tajik border while the lowlands to
west (which are close to the Kyzyl-Kum desert) and the
narrow parts of the Zarafshan valley between the two
mountain ranges are characterized by much lower precip-
itation rates. The discharge of the Matcha River is steadily
increasing from the headwaters down to the city of Aini
(D4) where it is joined by the Fondarya River and forms
the Zarafshan River. The impact of the aforementioned
water withdrawal for irrigation purposes downstream of the
Uzbek–Tajik border can clearly be seen as well as the
actual discharge in the Uzbek part of the river remains well
below the potential natural discharge as it would be
determined by the precipitation and evaporation rates in
this arid region.
Downstream of Samarkand (M5) the Zarafshan River is
split into two branches—the Ak-Darya and the Kara-
Darya—which reunite after 160 km near Yangirabod and
Khatyrchi (D8). The water diverted for the irrigation
farming is in parts drained from the fields and discharged
back into the river untreated. All in all 94,800 ha of irri-
gated land is drained and the total length of the drainage
water collector system in the Zarafshan catchment is
3,292 km. This return flow and the balancing impact of the
Kattakurgan reservoir on the Kara-Darya river branch lead
to a mitigated discharge hydrograph of the Khatyrchi hy-
dropost (D8) (Fig.
10
). The western parts of the catchment
are also heavily impacted by soil salinization. This leads to
an extensive leaching of the irrigated fields during the
winter months, which can be seen in the discharge hydro-
graph of the Navoi hydropost (D10).
Water quality
The anthropogenic impairment of the discharge regime and
the intensive water usage in the Uzbek part of the catch-
ment affect not only the quantity of the water resources but
also their quality. The mineralization is a very good
parameter to visualize the overall mineral load of the river
and the level of chemical degradation. Figure
11
shows an
exponential increase (
R
2
=
0.926) of the mineralization
from
the
Tajik–Uzbek
border
(P25—Ravathodja:
243.1 mg/l) to the official end of the Zarafshan near
Ghijduvan (P48: 1,799.0 mg/l) measured during the field
campaign in May 2010. The discharge during that month
was slightly higher than the average for that month
(173.6 m
3
/s in 2010 versus 166.9 m
3
/s at the Ravathodja
station), which coincides with the heavy rainfalls and flood
events in the upper parts of the catchment. This of course
influences the mineralization of the river as well as the
season in which the samples were taken. But as the water
quality is influenced by the intense agriculture throughout
the year (irrigation and application of agrochemicals for
winter wheat and cotton from March to November and
leaching during the winter months) there seem to be no
Fig. 8
Monthly water withdrawal at the Ravathodja station (D5)
Environ Earth Sci
123
phases where the pollution is significantly lower than
during the time of the field campaign presented here. This
also shows in the long-term data from the UZHYDROMET
which display a similar increase of the mineralization in
the Uzbek part of the catchment. The long-term minerali-
zation in the lower Zarafshan catchment is high enough to
exceed the Uzbek threshold of 1,000 mg/l. The minerali-
zation in the Tajik part of the catchment on the other hand
Fig. 9
Gradual change of meteorological and hydrological parameters in the Zarafshan
Fig. 10
Seasonal discharge in the lower Zarafshan catchment
Environ Earth Sci
123
was very homogeneous at all sampling points with con-
centrations between 161 and 188 mg/l.
This high mineral load of the river in the lower part of the
catchment has considerable effects on the usability of this
water. Especially the rural population living along the Za-
rafshan and the irrigation canals is using the river directly as
their source of drinking water and the data suggests that this
practice could lead to increased health risks downstream of
Navoi. Furthermore the mineral content in the water con-
tribute to the salinization of the irrigated fields and the
pollutants might accumulate in the crops grown.
The UZHYDROMET data can also be used to estimate
the total mineral load of the Zarafshan. At the Ravathodja
station (U1), the total load between 2002 and 2010 was
1.42
9
10
9
kg/year. 200 km downstream, at the conflu-
ence of the Ak-Darya and the Kara-Darya River branches
(U5—Khatyrchi), the total load during that time period was
only 0.67
9
10
9
kg/year. This reduction in the overall
mineral load of the Zarafshan can most likely be explained
by the Kattakurgan reservoir and its function as a sediment
sink. Downstream of Navoi (U7) and 100 km downstream
of Khatyrchi the total mineral load increased again to
0.9367
9
10
9
kg/year and there are two main sources for
this mineral input. The city of Navoi is not only an urban
agglomeration with approximately 125,000 inhabitants but
also the site of the Navoi special economic area. One of the
biggest companies located here is Navoiyazot, the largest
manufacturer of mineral fertilizers in Uzbekistan. The
second source of mineral input is the aforementioned return
flow from the irrigated fields. This drainage water is loaded
with fertilizers and pesticides during the vegetative period
and dissolved salts from the leaching during the winter
months and is characterized by a very high mineral load.
The average mineralization in the drainage water collectors
sampled during the field campaign in 2010 was 2,235 mg/l
and the highest mineralization detected was 2,594.8 mg/l
(at P43 downstream of Navoi), which is more than 2.5
times the national threshold.
Among the agrochemicals, nitrate and phosphate are the
substances with the highest concentration in the river
water. During the 2010 field campaign, the nitrate fluctu-
ated within the Tajik part of the catchment, but the con-
centration stayed well below the threshold for potable
water of 50 mg/l. In the Uzbek part of the catchment,
however, the nitrate concentrations quickly reached con-
centrations of up to 75 mg/l (Fig.
12
). The highest nitrate
concentrations in the Zarafshan were detected in the Ak-
Darya river branch and downstream of the Navoiyazot
waste water inflow. The concentration in the Kara-Darya
river branch was much lower and did not exceed 25 mg/l.
The long-term data from the UZHYDROMET also shows
an increase of the nitrate pollution in the lower catchment,
but no threshold exceedance.
Despite the long-term data not exceeding the threshold
the annual total load of Nitrate downstream of Navoi is
8.45
9
10
6
kg very high and equals an annual loss of
nitrate of 15.65 kg per irrigated hectare in the Uzbek part
of the Zarafshan catchment.
Fig. 11
Mineralization of the Zarafshan River
Environ Earth Sci
123
The phosphate concentration showed a different pattern
during the 2010 field campaign. While the Uzbek part of
the catchment was characterized by an increase of the
phosphate pollution from the border to the official end near
Ghijduvan, the highest concentrations were measured in
the upper regions of the Zarafshan River. This punctual
high phosphate load was most likely caused by the heavy
rainfall in the Tajik part of the catchment and the thereto
related intensified soil erosion.
Soil erosion is an important problem in the mountainous
regions of Central Asia, especially on slopes of southern
exposition and overgrazing on marginal lands has been
identified as the main cause for this process (Akhmadov
2003
; Breckle
2003
; Schickhoff and Zemmrich
2003
;
Wolfgramm et al.
2007
). In Tajikistan soil erosion often
occurs in the form of hazardous landslides of which 50,000
were reported by the Taj Glavgeology during the 1990s
(Barbone et al.
2010
; UNDAC
2006
). In the Tajik part of
the Zarafshan catchment landslides, floods and mudflows
are a major concern and cause significant losses of live-
stock, damage the infrastructure and can lead to casualties.
The most active season is the late spring from April to June
(Saidov
2007
) and the most active areas within the catch-
ment are the slopes of the Gissar and Turkestan ranges
(UNDAC
2006
) between Aini and Pendjikent. This is
exactly when and where the highest phosphate concentra-
tions were registered during the field campaign. Members
of the German Agro Action in Pendjikent reported that the
rainfalls prior to the WAZA CARE field campaign lead to a
mudflow destroying several houses and killing cattle in the
midstream region between Aini and Penjikent. Annually
between 500 and 1,000 t/km
2
of arable topsoils and
Fig. 12
Nitrate and phosphate concentrations along the Zarafshan River
Environ Earth Sci
123
nutrients are lost in the upstream parts of the Zarafshan
catchment (Fig.
13
).
The pollution in the Uzbek part of the catchment is most
likely caused by urban waste water inflow from the Sa-
markand metropolitan area and the Navoi municipal and
industrial waste water. The long-term data from the UZ-
HYDROMET indicates again lower concentrations, but the
main sources Samarkand and Navoi can be easily identified
as well.
Even more important than the urban and industrial waste
water inflow is the drainage water from the irrigated fields.
The samples from this category of water bodies showed the
highest average nitrate and phosphate pollution with
maximum concentrations of 175 mg/l for nitrate and
250 mg/l for phosphate (Fig.
14
). The analysis of the dif-
ferent water body categories also revealed that the mini-
mum concentrations for both parameters were much higher
in the artificial water bodies than in the natural ones. This is
an indicator for the intensive use of the irrigation canals
and the drainage water collectors by the rural population,
small-scale discharge of waste water and non-point pollu-
tion from the irrigated fields.
Fig. 13
Soil erosion rates in the mountainous regions of Central Asia (data: RAS
1963
, p. 39)
Fig. 14
Average, minimum and maximum nitrate and phosphate
concentrations in different water body categories
Environ Earth Sci
123
These results are insofar alarming as the rural population
living in the irrigated areas uses the untreated water from
the irrigation canals as their primary drinking water source
and the drainage water is used for further irrigation by
downstream water users. This is necessary as the water
demand in the Zarafshan catchment is higher than the water
availability and the untreated drainage water is the only
source of additional water to close the annual gap of
1.6 km
3
of water needed for maintaining the status quo.
While the agrochemicals from the irrigation farming in
the Uzbek part of the Zarafshan catchment are the most
important pollutants, two other sources for the impairment
of the water quality are relevant. The first one is seen in the
Anzob ore mining and processing complex located in the
upper Zarafshan catchment at the Yagnob River (a tribu-
tary to the Fondarya River), resulting in a heavy metal
pollution of the Zarafshan. The second source is the urban
and industrial waste water from the cities Samarkand and
Navoi, leading to increased concentrations of petroleum
products, phenols and fluorine. Figure
15
shows the con-
tamination of the Zarafshan River with several of these
pollutants based on long-term data from the UZHYDRO-
MET. Unfortunately, the spatial and temporal resolutions
of the data in the Uzbek part of the catchment are not high
enough to come to definite conclusions about the impact of
the urban and industrial complexes and there is no data
available for the Tajik part of the catchment. A broader and
deeper research approach would be needed for a thorough
interpretation of the status quo in this regard and such a
field study should be considered for future research activ-
ities. But the results as they are never the less reveal some
interesting trends and emphasize the difference in scale
between the pollution of the Zarafshan River with agro-
chemicals and with industrial and municipal wastewater.
Furthermore, these pollutants might have a major impact
on the aquatic biocoenoses as they can be already toxic at
very small concentrations. The basic analysis presented
here will, therefore, be helpful for the interpretation of the
faunistic research done within this study as well.
Arsenic was the only pollutant analyzed here which
showed a very high concentration at the Tajik–Uzbek
border with rapidly decreasing values in the Uzbek part of
the catchment. Toxic concentrations of arsenic are causing
several severe illnesses such as dermal lesions, anemia or
liver damage (Patrick
2003
) and the concentration of up to
2.7 mg/l exceed the WHO threshold for arsenic (0.1 mg/l)
by far. Only 200 km downstream of the Tajik–Uzbek
border does the arsenic pollution fall below this threshold.
Fig. 15
Concentrations of urban and industrial pollutants along the Zarafshan River
Environ Earth Sci
123
This suggests that the Arsenic concentration in the Tajik
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